This invention relates to extended life sputtering targets and a method for using these extended life sputtering targets.
Sputtering is a process that coats semiconductor wafers or other substrates within inert-gas-filled processing chambers. These chambers contain sputtering targets and an electrically biased wafer adjacent the sputtering target. An electric field within the chambers ionizes the inert gas and dislodges atoms from the target to deposit sputter target material on the wafer. Typically, processing chambers may contain magnetrons that generate annular groove patterns in portions of the sputtering targets. Unfortunately, these grooves can dramatically shorten a sputtering targets"" life. Furthermore, the adverse effect of these grooves tends to become exaggerated for targets having increased diameters.
Several patents disclose raised rings or surfaces for increasing target life. For example, Strauss et al., in EP Pat. Pub. No. 1 087 033, disclose sputtering targets having two spaced annular rings. These rings correspond to target areas that experience the greatest erosion during sputtering. Daxinger et al., in U.S. Pat. No. 6,068,742, disclose a reversible sputtering target. Each side of this target contains two circumferentially-shaped protrusions designed to increase target life. Masahura, in Japanese Pat. Pub. No. 4-173965 discloses a target containing a single projection ring. The projection ring has a smooth surface to prevent re-sticking of target material and a rough surface adjacent the smooth-surfaced rings. This combination decreases dusting effects over the sputtering process"" entire life.
Recently, a ring-enhanced design has proven effective for sputtering layers used to construct memory chips. Since memory chips typically contain only two metal layers, film uniformity is not critical for these memory applications. Unlike memory chip applications, logic chip applications often require greater film uniformity. Unfortunately, targets containing ring-enhanced designs fail to produce the stringent film uniformity required for some logic applications. This may result from the increased number of layers deposited or the device design rules. Furthermore, since there are more metal layers in logic applications, poor uniformity becomes accentuated with each succeeding layer when a manufacturer skips chemical mechanical polishing (CMP) of the deposited layers. As the stacked film uniformity decreases, photolithography on the upper layers becomes more difficult.
Film uniformity is also important from a device fabrication standpoint. There is often some degree of over-etch when etching the device. If the etching is greatest in the wafer""s center and the film is thinner in the center, then there is an increased possibility of device yield loss.
Furthermore, a lack of uniformity has a pronounced effect on film thickness and sheet resistance uniformity for large targets, such as those having a diameter in excess of 250 mm. In these large diameter targets, the rings can have a negative impact upon a target""s useful life. As far as known, none of these ring-enhanced designs has received commercial acceptance for stringent device applications due to the above uniformity issue or other sputtering-induced defects.
The sputtering target has a design for uniformly depositing a material on a substrate. The target contains a circular disk; and the disk has a radius and a top surface. The top surface has a center region within the inner half of the radius, an outer ring-shaped region within the outer half of the radius and a base region separating the center region from the ring-shaped region. The outer ring-shaped region has a projection height for extending the life of the sputtering target. The center region has a projection height of less than the projection height of the outer ring-shaped region for increasing the sputtering deposition rate on the substrate adjacent the center region.
The method sputters a material on a substrate with a sputtering target or cathode. First ionizing an inert gas adjacent a cathode in a sputtering chamber prepares the chamber for sputtering. The cathode has an initial wafer to cathode spacing and a second wafer to cathode spacing for uniform sputtering. The second wafer to cathode spacing is greater than the initial wafer to cathode spacing. Dislodging atoms from the cathode with a rotating magnetron deposits a coating on the wafer using the initial wafer to cathode spacing. The initial spacing optimizes sputtering deposition uniformity for an initial period of time. Then dislodging additional atoms from the cathode with the rotating magnetron after the initial period of time deposits the coating on the wafer using the second wafer to cathode spacing. The second wafer to cathode spacing optimizes sputtering deposition uniformity during a second period of time.